Optical recording materials for storing information are known. One of the currently popular forms of optical storage of information is the compact disk or CD. Digital information is stored in the form of marks or with low specular reflectivity pits on an otherwise reflective background. In this format, the optical information is most often in the form of read only memory or ROM. Optical information is not usually recorded in real time but rather is produced by press molding. In a typical process, the optical recording substrate is first press molded with a master containing the digital information to be reproduced. The thus formed information is then overcoated with a reflective layer and then with an optional protective layer. In those areas having the deformations or pits, the specular reflectivity is lower than in those areas not having the deformations.
It is desirable to produce optical recording media which, when recorded in real time, produces a record that mimics CD-ROM on read out. Read out is at about 780 nm. In this manner, information can be added to the CD and the CD can be used on a conventional CD player.
One recently disclosed system of this type is the so called "Photo CD". In this system, conventional photographic film is first processed in a conventional manner. Then, the images from the film are digitized and the digital information is recorded in a CD readable form on an optical recording material. Images can then be played back by means of a CD type player on a conventional television. Since the Photo CD is not recorded to its capacity in a single session, or played back only once, long time multi session recording and play back capacity is needed. Thus, the need for very stable recording materials.
One method for forming a recordable element that mimics conventional injection pressed CD elements is to provide a support having thereon, in order, a layer of a dye that absorbs recording radiation and generates the needed change in the specular reflectivity and a reflective layer. Exposure of the recording layer through the support by the recording beam heats the recording layer to an extent that it is said that the surface of the heat deformable support just adjacent to the recording layer surface is deformed and the dye or dyes are changed to reduce specular reflectivity. Materials of this type are described in U.S. Pat. No. 4,940,618, European Patent Application 0,353,393 and Canadian Patent Application 2,005,520.
Commercially useful materials of the type described in these references have stringent requirements. One of these requirements is the long term stability of the recorded information on the Photo CD disks. So the materials used for the Photo CD disks must have very good light stability.